1. Field of the Invention
The present invention relates generally to valve gates and, more particularly, to a valve gate assembly for regulating a flow of molten material into a cavity of a mold.
2. Description of the Related Art
Injection molding is a widely known manufacturing process used to produce a variety of parts. Injection molding involves introducing a molten material, for example a molten plastic or resin, into a cavity within a mold until the cavity is filled. The molten material hardens in the mold in the shape of inner surfaces of the cavity. After the molten material hardens or cures, the hardened or cured material is removed from the cavity.
For injection molding, a manifold is typically used for conveying molten material from a central injection portion or sprue to a number of cavities or to multiple points within one large cavity of the mold. An example of such a manifold is disclosed in U.S. Pat. No. 4,964,795 to Tooman. In that patent, a manifold has a passageway through which a molten material may pass. The terminal end of the passsageway, called a gate, is in fluid communication with the cavity of the mold.
In addition, a valve nozzle or gate is typically used with the manifold to regulate the flow of molten material into the cavity of the mold. An example of such a valve nozzle or gate is disclosed in U.S. Pat. No. 5,996,618 to Saito. In that patent, a valve nozzle has a spool with a head portion, a shaft portion, and a coil spring, which presses the spool in the direction opposite to the gate such that when a resin pressure is less than a certain fixed level, the spool is pressed by the coil spring in the direction opposite to the gate such that it closes the gate and prevents the flow of molten material through the gate. However, when the resin pressure becomes higher than a certain fixed level, the spool overcomes a pressing force of the coil spring and is caused to protrude outward of the gate of the nozzle head, thereby causing the resin flow path to be opened.
It is desirable to provide a new valve gate that is urged in a closed position and opened without the use of an actuator. It is also desirable to provide a valve gate that has less parts. It is further desirable to provide a valve gate that is relatively cheaper to make. Therefore, there is a need in the art to provide a valve gate that meets these desires.